Coiled wire springs of both the compression and extension types have long been employed in the art for energy storage and for resisting or applying compressive or extension forces. In such types of springs the forces associated with longitudinal spring displacement essentially vary in a linear manner with attendant load displacement. In many instances however it is desirable to have the force associated with spring displacement vary in a predetermined nonlinear or nonuniform manner with attendant load displacement. An example of the latter is in the use of springs to help balance constant force loads. Mechanisms of various types have thus been long employed to position displaceable articles at selected locations intermediate terminal limiting positions thereof through the balance of constant force loads, such X-ray slide mechanisms and retractable article positioning. For example, counterbalance systems have long been employed in double hung window panels to maintain the selected positioning of a window panel at any location intermediate a fully open and fully closed position. One early example thereof was the use of pulley supported sash weights or the like. Counterbalance mechanisms of varying types in which a specific nonlinear spring rate assists in counterbalancing pivoting loads have also been used such as in automobile hood and truck lids, oven doors, and the like.
With respect to coiled wire springs however, and in a more fundamental aspect coiled wire compression and extension springs store energy within the spring metal during compression and extension by deflecting and straining the spring metal throughout the active length of the spring and provide a force that is normally proportional to the amount of longitudinal spring displacement. In other areas of coiled wire spring usage and particularly where space constraints and mass efficiency are not primary design considerations, coiled wire springs that are directly responsive to rotative displacement, i.e., spring biased hinges, mouse traps and the like, have been long employed. In many areas of compression and extension coiled wire spring usage it would be desirable to have the forces associated with longitudinal spring displacement vary in a predetermined nonlinear manner therewith and, that such nonlinear response characteristics could be of great utility in the counterbalancing of constant force loads.